Generally, semiconductor wafers are processed by surface-planing using chemical mechanical polishing (CMP) device.
The chemical mechanical polishing device polish oxide films or metal thin films applied on the semiconductor wafers using chemical and physical reaction, thus making the surfaces of the semiconductor wafers planar or removing the films therefrom.
As shown in FIG. 1, a representative example of the chemical mechanical polishing device includes a polishing head 5, a polishing pad 6 and a polishing agent supply unit. The polishing head 5 is connected to a motor and rotated by the operation of the motor. A wafer reception portion which contains a semiconductor wafer 7 therein is formed in a lower surface of the polishing head 5. The polishing pad 6 is located beneath the polishing head 5 and polishes the surface of the semiconductor wafer 7 contained in the polishing head 5. The polishing agent supply unit supplies a chemical polishing agent to the polishing pad 6.
Furthermore, a retainer ring 1 which forms the wafer reception portion is mounted to the lower surface of the polishing head 5.
The retainer ring 1 includes a mounting ring member 1 a which is mounted to a carrier of the polishing head 5, and a contact ring member 1b which is coupled to a lower portion of the mounting ring member 1a and is brought into contact with the polishing pad 6. Polishing agent supply groove are formed in a lower surface of the contact ring member 1b at positions spaced apart from each other.
The contact ring member 1b is coupled to the mounting ring member 1a by bonding using an adhesive.
The mounting ring member 1a is made of a metal, such as stainless steel (SUS). The contact ring member 1b is made of engineering plastic.
During the chemical mechanical polishing operation, the semiconductor wafer 7 is located in the wafer reception portion of the polishing head 5 and enclosed by a circumferential inner surface of the retainer ring 1 so that the semiconductor wafer 7 is prevented from being undesirably removed from the polishing head 5.
The chemical polishing agent which is in the form of slurry is supplied to the polishing pad 6 by the polishing agent supply unit.
The slurry type chemical polishing agent is supplied into the wafer reception portion through the polishing agent supply groove of the contact ring member 1b and oxidizes the surface of the semiconductor wafer 7.
The chemical mechanical polishing device repeatedly conducts the chemical oxidization action of the slurry type chemical polishing agent and the mechanical polishing action of the polishing pad 6, thus making the surface of the semiconductor wafer 7 uniformly planar.
However, the retainer ring 1 cannot reliably support the semiconductor wafer 7 because the bonding force between the mounting ring member 1a and the contact ring member 1b becomes weaker with the passage of time.
Thus, the surface of the semiconductor wafer 7 may become scratched during the operation of making the surface of the semiconductor wafer 7 planar.
Moreover, the semiconductor wafer 7 may break during the operation of making the surface of the semiconductor wafer 7 planar.
Furthermore, the retainer ring 1 is configured such that the mounting ring member 1a made of metal is exposed to the outside.
During the polishing operation, positive or negative charges are generated on the mounting ring member 1a made of metal, so that the chemical polishing agent in the form of a slurry more easily becomes stuck to the mounting ring member 1a. 
If the slurry type chemical polishing agent that has become stuck to the mounting ring member 1a hardens, when a subsequent polishing operation is conducted, it may be detached from the mounting ring member 1a, thus causing a defective semiconductor wafer 7.
Furthermore, the retainer ring 1 is problematic in that the mounting ring member 1a made of metal is corroded by the chemical polishing agent
In addition, the chemical mechanical polishing device has a membrane 8 which uses vacuum suction pressure to hold the semiconductor wafer 7 in the polishing head 5.
Chemical polishing agent inserts itself not only between the membrane 8 and the retainer ring 1 but also between the mounting ring member 1a and the contact ring member 1b and forms particles. The sizes of the particles increase over time.
Some of the particles which come off the elements may scratch the surface of a semiconductor wafer 7 or crack it.